1. Field of the Invention
This invention relates generally to flat panel displays comprising spaced-apart anode and field emitter plates, and more particularly to a flat panel display assembly of such type utilizing novel spacer means.
2. Description of the Related Art
In the use of field emitter technology, a wide variety of flat panel display assemblies have been proposed by the prior art. In general, these display assemblies comprise spaced-apart cathode (emitter) and anode plates, wherein the emitter plate comprises a multiplicity of field emission elements which produce electron beams which are transmitted to the anode display plate, which may for example comprise an array of phosphor elements or other luminescent materials or members, which are luminescently responsive to the impingement of electrons thereon.
In the manufacturing of flat panel display assemblies of the above-discussed type, the respective emitter and anode plates must be readily fabricated in spaced-apart relationship to one another, and a variety of spacer means and methods have been proposed in the prior art to effectuate the required spaced-structural relationship between the plates.
More specifically, the spacer structure is a critical element in the development of large-area reduced-pressure flat panel displays, which is a practical obstacle to the convergence of other aspects of display technology, such as emitter sources and phosphors. The use of displays in a wide spectrum of applications, including defense, scientific, medical, educational, business and recreational usages, has proliferated, and yet the potential for additional applications and refinement in the conventional technology is substantial. With the proliferation of devices such as portable work stations, lap tops, palm tops, pen-based pads, video phones, cellular phones, digital high definition television (HDTV), etc., and the proliferation of world-wide multimedia networks and satellite direct access capabilities, the volume of available cyberspace information is staggering in amount, and the visual display appears to be the only device which is effectively poised to communicate in a quick and efficient manner the vast amount of available information to users thereof.
Concerning specific application areas of flat panel displays, applications such as portable equipment and miniaturized microelectronic devices require extremely small volume to viewing area ratios, which more generally are desirable in a wide variety of other applications. Lap top, notebook and pen-based computer devices require flat panel displays to constitute commercially viable devices. The current promise of digital HDTV may never be realized in many households if it demands space for a 100 cubic foot cathode ray tube (CRT) or rear-projection based monitor. A truly functional and affordable flat panel display technology is likely to displace virtually every other form of two-dimensional display, including those used in stereo pair generation for 3-D viewing.
Despite its promise, many alternative technologies including liquid crystal displays (LCD's), active matrix liquid crystal displays (AMLCD's), plasma displays, electroluminescent displays and vacuum fluorescent displays have been utilized as commercial alternatives to flat panels, but all of these alternative display devices fall far short of providing an optimum flat panel implementation. Major issues such as cost, power efficiency, viewing angle, brightness, and color purity diminish their utility; nonetheless, the demand for flat panel functionality is sufficiently great so that such serious limitations currently not only are tolerated, but successfully compete with traditional display technology.
Field emitter array (FEA) displays provide a new display technology that is at least theoretically capable of meeting all of the requirements for a general purpose flat panel display. Advantages of FEA display technology include thinness of the panel (no bulky CRT tube and yoke, or back light, is required), low weight characteristics, wide viewing angle capability, wide range of color viewing capacity, high efficiency (direct light generation, cold cathode electron source means), high brightness, high resolution, very fast response time, wide dynamic range (from night levels to direct sunlight visibility), wide temperature range operating capability, instant turn-on character, back site component mounting ability, and reduced cost (being less expensive and much simpler in structure than the AMLCD).
Although the art has directed considerable effort to basic structures, materials, and manufacturing processes necessary to produce emitters for display purposes, unfortunately the critical spacer structure has not received a significant amount of attention.
Display structures using field emitters require a sufficient distance between the emitter (cathode) and the phosphor plate (anode) to isolate high anode voltages used to achieve the most efficient excitation of the light-generating phosphors. Spacing dimensions on the order of from about 0.5 mm to about 1.5 mm are typical. These spacing dimensions, while seemingly small, are in fact very large compared to the mean free path of electrons in atmospheric pressure gases between the respective cathode and anode plates. As a result, the spacing between plates must be evacuated to the pressure levels found in typical CRT's. Other flat panel display technologies also require partial (plasma displays) or comparable (vacuum fluorescent displays) levels of evacuation. Evacuation of the space between the cathode and anode plates places a one atmosphere (760 mm) static load on the plates and produces a plate deflection that is dependent on the area, strength and thickness of the material of construction of the plate, typically glass. Excessive deflection may seriously adversely affect the operating characteristics of the flat panel display, in such respects as pixel size, uniformity of brightness, and may increase the risk of anode to grid or cathode arcing. For small displays, such deflection is not a problem of significant character, due to the dimensions involved. Typical glass thicknesses of 2-3 mm may be used in perimeter-supported displays of up to 50 mm and potentially higher dimensions, but for larger area display articles, the corresponding need to increase plate thickness to accommodate such pressure levels would substantially add to the thickness and weight characteristics of the overall display and is not considered acceptable or desirable for commercial and aesthetic reasons. Accordingly, for larger area displays, internal spacer means are necessary to prevent undue deflection with the consequent adverse effects on operability, it being recognized that excessive pressure deflection in the absence of suitable spacer (support) means in the interior volume of the flat panel display article may result in rupturing of the evacuated plate and loss of its utility for its intended purpose.
The plate spacer structure introduces a number of structural and design complexities to the fabrication of the flat panel display article. The spacer structure must be strong enough to support the static pressure load, as well as any additional dynamic load resulting from handling, assembly, and use of the display. Further, the spacer structure must be fabricated to fit between pixels or pixel arrays (e.g., triads of color sub-pixels). The spacer structure further must stand off (insulate) the high anode potential. The spacer structure additionally must provide a continuous open pathway parallel to the plates to allow both initial evacuation of the display panel article, and long-term gettering of slowly released gas contaminants (off-gassing in situ in the interior volume of the display panel).
From a design standpoint, the spacer structure must permit alignment to the emitter (cathode) pixel structures, as well as to the anode plates phosphor color patterns in color display articles. The spacer structure must also be cost-effective in fabrication and assembly.
The foregoing requirements present a great challenge in the development of commercially acceptable, mass-producible flat panel display articles that are field emitter-based, and provide medium to large area display capability.
Currently practiced spacing means and methods have associated severe shortcomings. One field emitter display article prototype devised by LETI in France, utilizes glass spheres which are adhered to the emitter plates with a screened-on organic adhesive medium. The spherical spacer elements are undesirable because their aspect ratio (1:1) do not satisfy the requirements of higher resolution displays and their shape increases the potential for arcing between the anode and the grid or emitters. Organic adhesives also are undesirable because of the associated high temperature sealing conditions required, evacuation bake requirements during pump-out, long-term outgassing loads in the small volume static vacuum space, and because the low dielectric constant of the organic adhesive at the interface promotes splash-over.
The use of cured photosensitive polyimide spacer blocks formed directly on the emitter plate from 100 micrometer-thick films has been proposed. This technique also is severely limited in aspect ratio-characteristics, and long-term outgassing properties of the polyimide material in small high vacuum assemblies has not been demonstrated.
Other plasma displays have been produced using tall, vertically-standing metal wire segment spacers. The insulated AC operation of these panels allows the use of these metal spacers which are individually placed on an adhesive material, in a standing position, but they are unacceptable for field emitter displays. The maintenance of spacers in a precise vertical position during the fabrication operation is a difficult and yield-limiting task. Although contamination is less of a problem in plasma display applications which work in a moderate pressure gas environment, the contamination associated with the use of such adhesive material with the metal spacers is highly undesirable in field emitter-based panel article applications.
Accordingly, none of the aforementioned conventional spacer techniques satisfies the requirements of high performance vacuum panel displays.
It therefore is an object of the present invention to provide a means and method of spacing emitter and anode plates in a field emitter-based flat panel display assembly, which overcomes the aforementioned various disadvantages of the prior art spacer means and methods.
It is another object of the present invention to provide such improved spacer means and method, which are effectively utilized in large area display panel applications.
It is a further object of the present invention to provide such improved spacer means and method which are non-deleterious to the pixel arrangement and operation of the display panel.
Other objects and advantages of the present invention will be more fully apparent from the ensuing disclosure and appended claims.